Spark-plug construction



April 28, 1942. G. M. PAuLsoN SPARK PLUG CONSTRUCTION Filed Aug. 21, 1940 IN NToR BY ,l l

ATToRl-:v

||||Il|||||| l IIIIIIII to mica-insulated spark-plugs.

Patented Apr.l 1942 UNITED STATES PATENT OFFICE 2,230,972 seaux-PLUG vcoNs'rnUc'rmN George M. Pannen, New Yori, N. Y. Application amm zi, 194e, semi No. 353,445 a (ci. 12s- 169) 12 Claims.

'I'his invention comprises an improved sparkplug construction.

The invention relates more especially to radio-shielded plugs, and to those capable of service in aviation engines.

It is an object of the invention to provide an improved spark-plug which has relatively few parts and in which there is little possibility of electrical leakage.' Another object is to provide a shielded-type spark-plug construction which may be of reduced over-all length without reduction in the length of possible electrical leakage or flash-over paths, or which may be of conventional length with longer possible electrical leakage or flash-over paths.

In a more specific aspect, the invention relates struction in which a mica sleeve or cigarette, which is disposed around the spindle, can be wound more tightly without injury to the mica. It also affords a construction in which a closer fit can be obtained between this mica sleeve and a stack of mica washers in the lower portion of the plug. An advantage of tight wind of the mica cigarette, and likewise of close fit between the cigarette and the washers,-is the elimination or minimization of electrical leakage through ionized air, or other gases.

Another object of the invention is to eliminate the localized compression heretofore applied to the mica sleeve or cigarette to prevent gas- I leakage.

Another object of the invention is to provide a construction which is advantageous in respect(- to the dissipation of heat.

Other objects, features and advantages of the' invention will appear or bepointed out as the specication proceeds.

In the accompanying drawing, forming a part hereof: p

Fig. 1 is a longitudinal sectional view of a spark-plug made in accordance with this invention.

Fig. 2 is a reduced-scale view, mostly in section, showing a conductor lead attached to the spark-plug of Fig. 1.

Fig. 3 is a sectional view illustrating the method of making the core assembly of the sparkplug shown in Fig. 1.

The spark-plug shown in the drawing has a metal lower body or shell I provided with ground electrodes I I, and an upper metal body I2 which threads into the shell III and compresses a gasket I3 against the top of the shell. 'I'he lower spark-plug construction, is sometimes referred to as a coupling nut. An opening Il through the upper metal body I2 tapers toward its lower end, i. e. the diameter of the opening Il becomes progressively smaller toward its lower end.

A downwardly tapering spindle I6 has a head Il, constituting a center electrode, welded to its lower end. This head is large enough to form an annular shoulder I9 on the spindle. An insulating sleeve or cigarette 2| of mica insulation, tightly wrapped, is directly interposed between the tapered surfaces of the spindle I6 and the opening Il. This sleeve or cigarette extends from the shoulder I9 to the top of the part I2 of the body of the plug.

An additional body of insulation, preferably consisting of a stack of mica washers 22, is held under compression between the shoulder I8 and a recessed face at the bottom of the body part I2, and closely surrounds the lower portion of the mica cigarette 2l.

part of this upper body corresponds to what, in

The spindle I6 preferably consists of a tube I1 of steel or other suitable metal, which tapers both outside and inside, and a tapered insert 23 of copper or other material of relatively high heat conductivity. Such inserts aid in conducting heat away from the center electrode I8, and

Lthe upwardly increasing section of this spindle facilitates heat conduction and radiation.

The upper end of the spindle I6 terminates well below the upper end -of the body I2, leaving a shielding barrel 24 at the upper region of the spark-plug, lined by the insulating cigarette 2|, to receive an insulated conductor 21 shown in Fig. 2. 'I'he conductor includes wires 25 surrounded by insulation 26, which terminates lsome -distance back from the ends of the wires and is tapered along its lower portion to` t into the tapered socket of the barrel.

Matters relating to the conductor or lead 2l and its electrical contact with the spindle I6 are not novel in this invention but will be described briefly. A tube 28 of paper-base Bakelite or similar material is disposed around the part of the conductor insulation inside the barrel and preferably holds an annular disc 29.` The wires 2i extend through the disc 29, and through a ferrule Il, and are bent back around the ferrule. A spring 32 held by the ferrule 30 serves as the electrical connection between the wires 25 and the conductor immediately above the spark-plug,

and there is another coupling 38 at the otherendof the elbow for` connection with a metal Jsheath (not shown) forA shielding the remainder insulation 2l ,and 22.

An important feature of the method is that the insulation 2|, 22 is associated with the spindle, or the spindle element I1 before the head I8 is welded to the spindle, and is in place'when the, Y

^ welding operation is performed. This makes unnecessary a subsequent machining 'operation to remove externaljiiashor extruded metal, at the junction between the spindle and the spindle 1 head. f In former practice, spindle heads were fweldedrtmspindles before the insulation wasapplied, and it was necessary to machine away-the flash in order that, thereafter, the insulation might make a good fit with the lower end of the spindle and the shoulder of the spindle head. Inv the method of this invention the small amount of flash that'is formed tends to ll any airspace that there may be at this region, and to that extent is beneficial.

The method of assembling and securing the core elements will now be more particularly described, but it will be understood that details may be varied.

. The stack of washers22 is' placed in a clamp-A ing nut 40,which does not form part of the spark-plug. This nut ,and the body element I2 are then screwed together, the nut engaging the threads which later connect the Ibody I2 with the lower body or shell I0. The stack of wash'- ers is held in position, and is tightly compressed endwise of the stackbetween a shoulder 50 in the clamping nut and the recessed end face of the body I2. The bore'of the stack of washers is taper reamed sothat it will fit the tapered cigarette.

I6. Thismandrel with the cigarette on itis inserted into the tapered opening of the body I2 and-the'tapered bore of the stack of washers.

The mandrel is"v then removed, leaving the cigarette in place. At a suitable time the ends of the cigarette are trimmed. i

Now the hollow spindle element I1 is inserted into the cigarette. The parts are then as shown in Fig. 3. This assembly is placed on an elecr,

tric resistance welding machine by slipping the spindle element Il over a tapered'electrode I2 of the Welding machine.- The spindle head I8 is ,held by achuck 43, which is the second electrode of the welding machine. One or both of the electrodes `of .theI welding machine move toward and from the other in a manner well unf `derstood ln .the art, and the opening in the end of the clamping nut 40 serves as a guide for accurately positioning the head I8 with respect to the hollowspin'dle asthe two are brought togetherA forv welding.

The spindle head is pressed forcibly against the end! of the hollow spindle and the current is turned on. The heat and pressure cause lmetalto flow forming a certain amount of external flash which is accommodated by the mica insulation and helps to close any air space.l However,

the amount of -fiash is relatively small, and not sufficient to injure the insulation, since the stack The cigarette 2| is `tightly wrapped about a mandrel having the same taper as the spindle of washers 22 acts as a. stopv for the` head Il in the welding operation and limits the amount'of metal that is extruded. The pressure' on the spindle head in lthe welding operation places j some additional compression on the stack of washers, though this n'eed notbe the case. In

any event the stack is now clamped between the head la and the body n.

. 4The assembly is then removed-from the elec- I trode l2, and the nut 40 is removed from the body I2. -The stack of washers is then preferablymachined to the external taper shown in Fig. 1. The insert 23 is driven into the ,hollow-spindle element I1.

When the body I2 is screwed into the shell I0 the construction of the spark-plug proper is come plete. l

In former practice it was customary to wrap a mica cigarette about a cylindrical spindle having either an integral head or a head united to the spindle before thecigarette was wrapped.

In that operation it wasnot easy 4to get a good t between the lower end of 'the cigarette and the shoulder of the head. With the construction and method which have beenV described ine.Y

this specification the cigarette need not be wound with its end against a shoulder. In the welding operation the shoulder of the head is brought tight againstthe lower endof the cigarette as well as against the lower end of the stack of mica washers.

Because of the tapered construction the mica I cigarette can be more tightly wrapped than the customary cylindrical cigarette, also a tighter fit can be obtained between the cigaretteand the bore of the stack of washers.A ,In the core-as-l se'mbly the cigarette is held tightly between the tapered spindle and the tapered opening in the body I2. It is tight against the washers and tight against the spindle head'. l v

For full disclosure the preferred embodiment of the invention hasA been described in detail, but

- it will be understood by those skilled in the art that details may be varied and that there may be substitutions of material.

Advantages ofthe inventionmay -be readily comprehended by comparing the construction shown and 'described herein with'that disclosed in Patent 1,930,322. It will be observed, for example, that I have' succeeded in eliminating one mica cigarette and a top stack of mica washers, and two of four possible electrical leakage paths,

also a soft metal cone with its compressive meth-l od of sealing against gas leakage. Other advantages and improvements have been pointed out.

The body of insulation 22 is preferably composed of a 'stack of mica washers, as herein described. However, the invention, in a broader aspect, is not necessarily limited to-this type of insulation, since insulation of other material 0r construction could V be substituted;

Terms of orientation, such as upper and lower,

'I refer to the position ofI the spark-plug `shownl in the drawing, not to the position which it may occupy in use. The lower end of the spark-plug` is the inward endin relation to the .engine cylinder, and the upper end is the outward end.

vI'claim:A

1,-In a spark-plug, a coupling nut having a dswnwardly tapered opening, a tapered spindle held in said opening and extending downward from the coupling nut, a shoulder on the spindle, and insulation clamped between the shoulder and -a surface of the coupling nut and holding the spindle against upward displacement in the cou-- pling nut.

2. A spark-plug including a lmetal body in which is an opening that ltapers toward its lower end, a tapered spindle in the opening, a sleeve of insulating material around the spindle, a shoulder.` on the lower portion of the spindle, and other insulating material clamped between the shoulder and a surface of the metal body.

3. A spark-plug including a metal body having an opening that tapers toward its lower end,

an insulating cigarette lining the opening, and a.

tapered spindle in the opening but coniined to the lower part of the opening so that there is an insulation-lined socket' in the metal body above the spindle to receive a conductor, the lower portion of said cigarette being interposed directly between the outside of the tapered spindle and the tapered inside of the metal body.

4. A spark-plug construction including a metal body, a tapered spindle therein, said spindle decreasing in cross-section toward its lower end,

opening and extending downward below `the metal body, a tapered spindle in the lower portion of the opening, leaving the upper portion of the opening'to serve as a socket for reception of a conductor, said spindle extending downward below the end of the metal body and having a shoulder near its lower end, a stack of insulating washers around the lower portion of the sleeve and compressed between the shoulder of the spindle anda surface of the metal body, rsaid washers and sleeve constituting the insulation of the core assembly.

9. A shielded spark-plug including a body the lower portion of which is threaded, said body having ya uniformly tapered opening with its largest diameter` at its upper end,-a mica sleeve lining said opening, a tapered spindle in the low'- er portion of the opening, leaving the upper portion ofthe opening to serve asa. socket for the reception of a conductor, said spindle and mica sleeve extending below the body, a shoulder on insulation 'surrounding' the lower part of the tapered spindle and contacting with 'a face of the metal body, a head connectedvto the lower end of Ithe, tapered portion of the spindle, and a shoulder formed by the head in position to clamp said insulation against said face of the metal body.

5. Aspark-plug comprising a shell, a spindle havinga head, a shoulder at the upper end of the head, the spindle above said shoulder increasing in V cross-section upwardly, a coupling nut threaded into the shell and `having a tapered opening in which the spindle is'held, and insulation surrounding the spindle and clamped between said shoulder and a surface of the coupling nut.

6. A 4core assembly fora spark-plug including a metal body with an' opening that tapers to a smaller size` toward the bottom of the metal body, a tapered spindle-held in the opening of the metal body, a sleeve of mica wrapped around the spindle and insulating said spindle from the sides of the opening in the metal body', other insulation around a portion of the spindle and below a surface of the metal body, and a shoulder on the lower portion of the spindle 'clamping said other insulation against said surface' and holding the spindle, insulation, and (metal body in assembled relation.

7. A spark-plug construction in which a downwardly tapered spindle is surrounded by an inf sulating sleeve and held securely in a tapered opening of a metal body by insulation compressed between a lower portion of body and a shoulder of the spindle.

8. A spark-plug core assembly comprising a metal body in which is a downwardly tapered opening, .a single sleeve or insulating material lining both the upper and lower portions of said the metal the spindle at the end ofthe mica sleeve, a stack of mica washers surrounding the mica sleeve and compressed between the shoulder and a bottom face of the body, and a shell into which said body is screwed.

` sulating cigarette interposed directly between `pered insidev of said body.

10. A spark-plug construction including a metal body having a downwardly tapered opening, a correspondingly .tapered spindle, and an insulating cigarette interposed directly between the tapered outside of said spindle and the tall. A vspark-plugv construction including a metal body having a downwardly tapered openinga correspondingly tapered spindle, an inthe tapered outside of said spindle and the tapered inside of said body, a head secured to the lower end of said spindle, and additional insulation about the lower portion of said cigarette and held under compression between said head and said body.

12. A shielded spark-plug construction including a metal body having a downwardly tapered opening, a downwardly tapered spindle occupying the lower portion of said opening, the upper portion ofl said metal body constituting a socket for the insertion of a conductor, a tapered insulating sleeve surrounding said spindle and directly interposed between the outside of the same and the inside of said metal body, said sleeve extending upward above said spindle to line said socket, a body of insulation having a tapered interior fitting the lower portion of said sleeve, and a head secured to the lower end'of said spindle in close contact with the lower ends of said cigarette and said body oi' insulation, said body of insulation being held tightly between the shoulder o! said head and the lower end of said metal body.

GEORGE M. PAULSON. 

